• P.K. Peterson

Escherichia coli 0157:H7 Lurking in Lettuce: Where’s the Beef?

“Nothing will benefit health and increase the chances of survival of life on Earth as the evolution to a vegetarian diet.” Albert Einstein

Just as I began increasing my diet of green, leafy vegetables, the Food & Drug Administration (FDA) announced the source of three outbreaks of Escherichia coli 0157:H7 gastroenteritis related to contaminated romaine lettuce. The outbreaks began on November 7, 2019, and by December 20, 138 people had been sickened in 25 states. Seventy-two of these patients had been hospitalized, and 13 were diagnosed with the dreaded hemolytic uremic syndrome (HUS). All three outbreaks were linked by the FDA to a common grower in Salinas, California.

Some readers of this blog may be surprised that a vegetable, such as lettuce, can be dangerous to your health. This may be especially true for those who remember something of the remarkable 1993 outbreak of E. coli 0157:H7 gastroenteritis related to undercooked hamburgers that were served in 73 Jack in the Box restaurants. That outbreak resulted in about 700 illnesses, 171 hospitalizations, and 38 children with kidney problems due to HUS, four of whom died. In a congressional hearing in 2006 sparked by the outbreak, Senator Durbin declared it a “pivotal moment in the history of the beef industry.”

What’s so special about E. coli 0157: H7, and where does it hang out? E. coli are very common bacteria in the gastrointestinal tract, where most are harmless members of the normal bacterial flora. Microbiologists estimate that there are 45 different strains of E. coli, including a group of 100 O serotypes that produce Shiga toxin (ST).

The main reservoir of ST-producing E.coli (STEC) strains is grass-feeding animals, cattle in particular. Their meat might become contaminated by fecal matter due to poor processing methods during slaughter, and their feces might end up contaminating other foods (e.g., vegetables) and water. Interestingly, STEC don’t cause disease in cattle, but their feces, spread as fertilizer in farm fields, serves as a major vehicle for contamination of vegetables and other foods.

A wide variety of food has previously been implicated in outbreaks as suspected sources, including raw (unpasteurized) milk and cheese, undercooked beef, several kinds of fresh produce (e.g., sprouts, spinach, and lettuce), and unpasteurized apple cider. Recently, an outbreak of STEC O157 infections in Canada and the USA was linked to walnuts, thus new sources continue to be identified.

While contaminated food or water is a common source of outbreaks of STEC, person-to-person transmission is also possible among close contacts (families, childcare centers, and nursing homes). What makes E. coli O157:H7 so dangerous, however, is its production of ST. While E. coli O157:H7 is by far the most notorious ST producer, many other E. coli O serotypes share this virulence factor.

It is the ST that is the culprit in causing most of the disease manifestations of E. coli 0157:H7, including bloody diarrhea (enterohemorrhagic colitis), hemolysis of red blood cells and uremia due to kidney failure, called the HUS. As in many infectious diseases, young children and the elderly are at greatest risk of these complications. But don’t blame the E. coli bacterium itself for its nastiness. Production of the toxin is under the control of a prophage (a genetic element from a virus acquired in the past).

How is E. coli O157:H7 infection treated and prevented? Fluid replacement and blood pressure support may be needed to prevent death in severely ill patients, but most victims recover without treatment in 5-10 days. Even though this is a bacterial infection, it shouldn’t be treated with antibiotics (antibiotics are thought to trigger prophage induction and make matters even worse).

Prevention requires common sense. Avoid foods that have been identified as suspect by the FDA or Centers for Disease Prevention and Control (CDC). Currently, that means romaine lettuce labeled as from Salinas, California. Practice proper hand washing after using the bathroom or changing diapers. Also, anyone with a diarrheal illness should avoid swimming pools or lakes, sharing baths with others, and preparing food for others.

Other foodborne germs and illnesses. The CDC estimates that each year 48 million Americans get sick from a foodborne illness, 128,000 are hospitalized, and 3,000 die. While E. coli is one of the germs responsible, it isn’t even among the top five pathogens: norovirus, Salmonella, Clostridioides difficile, Campylobacter, and Staphylococcus aureus (Staph). The same measures for preventing E. coli 0157:H7, however, apply to all of these enteric pathogens. And if you follow these recommendations, you won’t need to let the prospect of diarrheal disease ruin a good meal.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.


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© 2020 by Phillip K. Peterson
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